1. Field of the Invention
The present invention relates to radiation shielding material, and, more particularly to radiation shielding material fabricated with hydrogen, boron and nitrogen containing materials.
2. Description of Related Art
In space, the vehicle, crew, and scientific instruments are exposed to harsh environments including galactic cosmic radiation (GCR), neutrons, solar particle events (SPE), extreme temperature excursions, hard vacuum, neutrons and micrometeoroids. Materials for vehicles and spacesuits must possess functional characteristics of radiation shielding, thermal protection, pressure resistance, and mechanical durability. There is an existing need to develop new materials and composite layers that offer improved shielding against GCR, neutrons, and solar energetic particles (SEP) in the most structurally robust combination, also capable of shielding against micrometeoriod impact.
Radiation protection is an enabling technology for future exploration missions. Human missions greater than approximately 90 to 100 days beyond low Earth orbit (LEO) cannot be supported without developing shielding and/or biological countermeasures to remain below Permissible Exposure Limits. Adequate shielding measures are needed to enable safety of crew and hardware during long duration human missions up to 1 year in space. Hydrogen, boron, and nitrogen based materials can provide mechanically strong, thermally stable, structural materials with effective radiation shielding against GCR, neutrons, and SPE. Neutron exposure tests on boron nitride (BN) containing polymers and boron nitride nanotube (BNNT) containing polymers showed that they can provide great effectiveness for radiation shielding. However, the hydrogen content in the polymer matrix may not be sufficient to protect from GCR and SPE. By incorporating hydrogen into the BN and BNNT either by hydrogenation or hydrogen storage methods, highly effective radiation shielding materials can be realized against GCR, SPE, and neutrons. Lightweight durable multifunctional materials in all forms are needed for radiation protection for both humans and microelectronic components. Electronic components become more vulnerable to particulate radiation (including neutrons, protons, and heavy ions) as their size shrinks and the operating voltage is reduced. Microelectronics in future aerospace vehicles and medical applications, such as pacemakers, require effective lightweight radiation shielding materials such as transparent or nontransparent hydrogenated (or hydrogen stored) BNNT composite coatings or layers.
No other known experimental or computational studies have been done on the radiation shielding properties of hydrogenated or hydrogen stored BN and BNNT containing polymers. The prior art mostly uses high hydrogen containing material only, such as liquid hydrogen, water, or polyethylene. These materials alone, however, do not offer mechanical robustness or thermal protection for structural applications. Hydrogen content in water and polyethylene (known as highest hydrogen content polymer) may not be sufficient for long term space exploration for both humans and microelectronic components. The density of hydrogen is too low to be used for radiation shielding practically. In addition, hydrogen can slow down or scatter GCR, high energy neutrons, and SEP very effectively, but does not absorb neutrons very effectively compared with boron or nitrogen. Hydrogenated or hydrogen stored BN and BNNT materials can offer additional hydrogen content to the hydrogen containing polymer matrix against GCR and SPE while providing neutron shielding capability.
This innovation expands beyond the prior art and uses boron, nitrogen, hydrogen, hydrogenated or hydrogen stored BN and BNNT, and their combinations in the tailoring of radiation shielding materials for GCR, SPE, and neutrons. This invention uses modeling and experimental data to validate the model. There are a number of disadvantages to the prior art, in particular the inability to achieve very high effective cross sections of the shielding material. This necessitates the use of relatively large amounts of the filler material in order to be able to achieve effective shielding. The reliance on high hydrogen content brings with it problems including low material density (high liquid hydrogen volume required for effective shielding), lack of mechanical integrity, and flammability for some polymers. The use of micron size powders, as is currently described in the literature, leads to high filler volume fraction thresholds for effective radiation attenuation. This brings with it the problems of increased weight (the fillers are generally more dense than the matrix), increased cost, as larger amounts of neutron attenuating filler are required, very poor processibility as the filler volume increases and a drastic decrease in the other desirable properties of the resultant materials. Lead shields are extremely heavy because of lead's high density and they are not particularly effective at shielding against neutrons. Furthermore high energy electrons (including beta radiation) incident on lead may create bremsstrahlung radiation, which is potentially more dangerous to tissue than the original radiation. Lead is also extremely toxic to human health, leading to handling difficulties.
This invention also has applications for shielding radiation from nuclear propulsion systems, nuclear materials, nuclear reactors, nuclear accelerators, nuclear medicine, nuclear diagnostics, nuclear power plants, nuclear powered submarines, nuclear bombs, and dirty bombs.
It is a primary aim of the present invention to provide radiation shielding material fabricated with boron, nitrogen, hydrogen, hydrogenated or hydrogen stored BN and BNNT.
It is an object of the invention to enhance radiation shielding by the controlled addition and dispersion of hydrogenated or hydrogen stored BN and BNNT containing materials into a matrix (polymer or ceramic).
It is an object of the invention to achieve effective radiation shielding by homogeneously dispersing a hydrogenated or hydrogen stored BN and BNNT material (BN platelets, hot pressed BN, BNNT, BN particle containing high hydrogen polymer resins, BN nanofiber containing high hydrogen polymer resins, carbon fiber reinforced BN containing high hydrogen polymer resins, BNNT containing resins, and hydrogenated BNNT) into a matrix synthesized from a hydrogen containing polymer, a hydrogen containing monomer, or a combination thereof.
It is an object of the invention to achieve effective radiation shielding by homogeneously dispersing a hydrogenated or hydrogen stored BN and BNNT material (BN platelets, hot pressed BN, BNNT, BN particle containing high hydrogen polymer resins, BN nanofiber containing high hydrogen polymer resins, carbon fiber reinforced BN containing high hydrogen polymer resins, BNNT containing resins, and hydrogenated BNNT) into a matrix synthesized from a boron containing polymer, a boron containing monomer, or a combination thereof.
It is an object of the invention to achieve effective radiation shielding by homogeneously dispersing a hydrogenated or hydrogen stored BN and BNNT material (BN platelets, hot pressed BN, BNNT, BN particle containing high hydrogen polymer resins, BN nanofiber containing high hydrogen polymer resins, carbon fiber reinforced BN containing high hydrogen polymer resins, BNNT containing resins, and hydrogenated BNNT) into a matrix synthesized from a nitrogen containing polymer, a nitrogen containing monomer, or a combination thereof.
It is an object of the invention to provide a material for shielding against galactic cosmic radiation (GCR), solar particle events (SPE), and neutrons.
Finally, it is an object of the present invention to accomplish the foregoing objectives in a simple and cost effective manner.
The above and further objects, details and advantages of the invention will become apparent from the following detailed description, when read in conjunction with the accompanying drawings.